Tissues and cells from various sectors of the mouse prostate will be cultivated in specifically designed chemically defined culture media in organ and cell cultures. The roles of peptide and steriod hormones in growth and differentiation, and the responses to carcinogens, of these organized and unorganized tissue cultures will be studied in an effort to provide model systems for the study in vitro of prostatic hyperplasia and neoplasia. Inbred strains of mice, the accessory sex organs of which are known or suspected to be particularly susceptible to hormones and carcinogens, will be used, and aged mice will be examined for different degrees of spontaneous hyperplastic change and for possible neoplasms.